An image forming apparatus such as a copier, printer, or facsimile machine includes a large number of units and components. Even if one of the units and components in the image forming apparatus fails, the image forming apparatus does not work properly and a user is not able to use the image forming apparatus until the image forming apparatus is repaired. In view of this, various techniques have been proposed to predict whether the image forming apparatus is most likely to fail in the near future and to prevent the failure beforehand by repairing or replacing the unit or component of the image forming apparatus, for example, as described in Japanese Patent Application Publication Nos. H06-208265, 2005-309077, and 2008-102474. However, none of the above-described techniques predicts failure of a fixing device of the image forming apparatus, probably due to the difficulty in specifying one or more causes contributing to failure of the fixing device.